This study investigates mediation by macromolecules and filopodia of the interaction between foreign surfaces and blood. Platelet retention from native whole blood was minimal in "clean" (barely fused) glass bead columns under conditions for which retention is complete by both conventional glass bead columns and their siliconized equivalents. The poor retention was not due to inactivation or inhibition since the platelets were completely removed by a conventional glass bead column placed in series. Current findings showed that retention with these fused glass bead columns is: 1) increased only moderately after 30 min contact by gentle mixing or by reversing of flow in citrated whole blood at 37 degrees C; 2) not increased when the system is cooled to surface activate platelets; 3) not increased by 18 h contact with flowing, chromatography grade nitrogen at 95 degrees C or 22 degrees C; 4) greatly increased (complete) when preceded by placing a conventional glass bead column in the nitrogen stream at 95 degrees C but not at 22 degrees C, 5) duplicated by columns of loose, unfused "clean" (500 degrees C treatment) glass beads confined between short segments of fused bead columns. In addition, the platelets in the effluent from fused glass bead columns exhibit normal retention in a conventional bead column and also maintain the vascular integrity of the isolated perfused kidney.